Bees can sense—and learn from—the electric fields of flowers

Can zero in on flowers with specific electrical field shapes.

Flowers offer all sorts of cues to their pollinators—colors, patterns, shapes, and scents all help plants communicate with butterflies, bats, birds, and bees. But recent research suggests that another type of information—electrical fields—may work in concert with these other cues to provide extremely nuanced details about pollination status. This week in the journal Science, researchers show that this may play an important role in the extremely close-knit relationship between flowers and their pollinators.

As they travel through the air, bumblebees lose electrons, accumulating a small positive electrical charge. Flowers, meanwhile, are generally negatively charged at the top, thanks to a slight positive charge in the air around them. As a bee approaches a flower, a tiny electric field is created between plant and pollinator.

In the past, scientists have suggested that these differing charges encourage the transfer of pollen between flower and bee, helping the tiny pollen grains “jump” onto the pollinator. However, the new study showed that the bee’s landing actually influences the flower’s electrical charge—increasing it slightly—for a short period of time. The study's authors hypothesize that this change may signal to the next bee that the flower has just been visited and that its nectar stash is depleted. Other cues, such as a flower’s shape or color, sometimes change in response to a bee’s visit, but these changes can take hours. The electrical field, on the other hand, changes almost instantaneously, providing a nearly immediate signal to incoming bees.

In order for this process to work, bees must be able to sense the electrical fields of flowers. To test this ability, the researchers created a field of fake flowers that they could manipulate. Half the flowers were positively charged, and these flowers held a tiny bit of sugar solution as a reward for the bees. The remaining flowers had no charge and held a bitter quinine drink. After just 40 visits, the bees had learned that the positively charged flowers were rewarding, and they visited them more than 80 percent of the time. Once the charges were turned off, the visitation rate to the sugar-laden flowers decreased to random chance, since the bees no longer could use the electric field as a cue.

In a similar test, the researchers found that the bees could even distinguish between flowers that differ in the geometry of their electric field. The bees learned quickly that flowers with a “bullseye” electrical pattern—with a negatively charged center ring and a positively charged outer ring—were rewarding, while flowers with an even positive charge were not.

A final experiment with the artificial flowers suggests that electrical charges may work in concert with other floral cues to help bees learn. First, the researchers taught the bees that flowers of slightly different colors offered differing rewards; on average, the bees took about 35 visits to learn this rule. Then they conducted a similar trial but paired the differing hues with differing electrical fields. The bees in this trial were much quicker at picking up the pattern, learning the difference in about 24 visits.

From these experiments, it seems that electrical charge is not only a floral cue that bees can sense, but it also appears to help bees make better, faster decisions about which flowers to visit. It’s unclear exactly how bees can sense these electrical fields, but it’s possible that their tiny hairs can bristle up when exposed to positive charges, just as our hair stands on end in response to static electricity.

Kate Shaw Yoshida
Kate is a science writer for Ars Technica. She recently earned a dual Ph.D. in Zoology and Ecology, Evolutionary Biology and Behavior from Michigan State University, studying the social behavior of wild spotted hyenas. Emailkate.shaw@arstechnica.com//Twitter@KateYoshida